feat(v5.2.0): finalize Infrastructure & Polish (tests isolation, xdist, lint, CI)

tests/conftest.py: mutate the settings singleton (instead of rebinding) so DB + backup dir are isolated per test -> pytest-xdist safe.
Real backup tests (snapshot/prune/admin API) and OAuth mock tests (Gitea/GitHub/link) replace the previous skips.
init_db() now also creates webhook_subscriptions (full schema without the FastAPI lifespan).
ruff check is clean; .eslintrc.json migrated to eslint.config.mjs (flat config).
CI: lint job (ruff + eslint), parallel tests (-n auto), run on every branch push.
VERSION 5.11.1.

app/routers/api.py

@@ -149,7 +149,7 @@ async def move_card(
                 issue = await gitea.get_issue(owner, repo, issue_id)
                 current_labels = [lbl["name"] for lbl in issue.get("labels", [])]
                 status_labels = await _get_status_labels(owner, repo, board_id)
-                filtered_names = [l for l in current_labels if l not in status_labels]
+                filtered_names = [name for name in current_labels if name not in status_labels]
                 filtered_names.append(mapping["gitea_label"])
 
                 # Resolve label names to IDs
@@ -293,7 +293,7 @@ async def create_issue(
     if not _check_rate_limit(request):
         raise HTTPException(status_code=429, detail="Rate limit exceeded")
 
-    label_ids = [int(l) for l in labels.split(",") if l.strip().isdigit()] if labels else None
+    label_ids = [int(lbl) for lbl in labels.split(",") if lbl.strip().isdigit()] if labels else None
     milestone_id = int(milestone) if milestone.strip().isdigit() else None
 
     issue = await gitea.create_issue(
@@ -345,7 +345,7 @@ async def update_issue_api(
     if state:
         kwargs["state"] = state
     if labels:
-        label_ids = [int(l) for l in labels.split(",") if l.strip().isdigit()]
+        label_ids = [int(lbl) for lbl in labels.split(",") if lbl.strip().isdigit()]
     if milestone and milestone.strip().isdigit():
         kwargs["milestone"] = int(milestone)
     if assignee:
@@ -388,7 +388,7 @@ async def get_issue_detail(owner: str, repo: str, issue_id: int, format: str = Q
         comments = await gitea.get_issue_comments(owner, repo, issue_id)
     except Exception as e:
         logger.warning("Failed to fetch issue %s/%s #%d: %s", owner, repo, issue_id, e)
-        raise HTTPException(status_code=404, detail=f"Issue #{issue_id} not found")
+        raise HTTPException(status_code=404, detail=f"Issue #{issue_id} not found") from e
 
     # Get checklists from local DB
     with get_conn() as conn: